1. Technical Field
The present invention relates to a flicker detection device, a flicker elimination device, an image pickup device, and a flicker detection method. In detail, a screen is divided into a plurality of areas, addition of pixel levels and writing and reading of the result of the addition to a memory area allocated to each area are performed, the pixel levels in the area are accumulated for every area, and whether or not the area is a still image area is discriminated for every area using the result of the accumulation and an accumulation result of the same area which has already been stored in an accumulation result memory. Further, the accumulation results of the areas discriminated as still image areas are averaged, and a flicker level is calculated for every screen based on the averaged accumulation result and the accumulation results obtained by accumulating the pixel level in each of the areas for every area, thereby removing flickers.
2. Related Art
In the case in which image pickup is performed under a light source periodically turning on and off such as a fluorescent light, there are caused periodical bright and dark fringes on the pickup image or periodical differences in brightness of whole image between the frames. These are called flickers, and considered to be an inevitable problem under the blinking light source for image pickup devices equipped with image sensors accumulating charges to generate video signals.
In an image sensor, there can be different charge accumulation timings for every plane or for every line, and a method of synchronizing the charge accumulation timings for every plane is called a global shutter method while a method of synchronizing the charge accumulation timings for every line is called a rolling shutter method.
In the global shutter method, if the image pickup rate is higher than the blinking frequency of the light source, the amount of charge accumulated in a frame period varies between the frames, which may cause a flicker.
FIG. 7 is a diagram for explaining the charge accumulation amount in the image sensor adopting the global shutter method. In the case in which the illumination intensity IL periodically varies as shown in FIG. 7 in accordance with the frequency of the commercial power supply voltage, the difference in phase between the periodical illumination intensity and the exposure period causes the area difference between the hatched areas with a constant exposure period TC. The area of the hatched area corresponds to the charge accumulation amount, and accordingly, the difference in the areas, namely the difference in the charge accumulation amount, causes the difference in brightness between the frames. Therefore, as shown in FIG. 8, the frames with different phases from the illumination intensity IL form a video image with a brightness difference between the frames, and periodical differences in brightness of whole image between the frames appear. It should be noted that in FIG. 8 shows the case in which three frame periods correspond to one cycle of the illumination intensity variation.
A flicker component included in the video image shot under the periodically blinking light source can be approximated by a sine wave, and a method of removing the flicker utilizing the characteristics of the sine wave to form a correction image is adopted. Further, a method of detecting the flicker component from the input image and controlling the gain based on the detected flicker component in order for correcting the flicker has been proposed (see, for example, JP-A-2004-222228).